1. Field of the Invention
The present invention relates to a coding unit for a MPEG4/H.263 video coder, and more particularly to an adaptive DCT/IDCT (Discrete Cosine Transform/Inverse Discrete Cosine Transform) apparatus based on energy, for processing DCT and IDCT operations with a high image quality at a high speed by calculating energy of an input image in block units, and a method for controlling the same.
2. Description of the Related Art
A mobile communication service began with the first-generation analog service, and has gradually developed from the second-generation digital communication service to the third-generation IMT-2000 service. The IMT-2000 service is a communication service for enabling the next generation mobile communication terminal using standard technology proposed by ITU-T (International Telecommunications Union—Telecommunication). The IMT-2000 service enables users to receive a variety of services such as a voice phone service, a telex service, a pager service, and an E-mail service, etc., anywhere in the whole world. Current mobile communication services such as a cellular or PCS phone service for mainly providing users with voice services are being developed for the IMT-2000 service for supporting multimedia personal communications such as high-speed data, packets or images.
The IMT-2000 mobile terminal provides users with global broadband roaming service at a high speed, displays moving images on its own screen with a VOD (Video On Demand) scheme, and enables the users to exchange their images via a camera mounted to the terminal.
Therefore, the IMT-2000 terminal is of importance to a multimedia application service processor rather than a modem function. So, a chip and an additional memory for processing the multimedia application service besides a modem chip are needed to implement a wireless video mobile communication service with an optimal amount of processing capacity and a minimum amount of errors.
The development of the compression technology for storing/transmitting the large amount of data and standardization thereof are needed to implement the aforementioned audio and moving image services. The digital image technology has been developed from still images to moving images, and therefore the fundamental basis for multimedia services has been established.
In the meantime, the MPEG (Moving Picture Experts Groups) standardization has started to compression-store the moving images in a storage media.
There have been proposed a variety of established standardizations such as a H.261 recommended by the ITU, an MPEG-1, a MPEG-2, and a H.263 recommend by the ITU. The H.261 is used for a video telephone or video conference service with a transfer rate of 64 kbps˜2 Mbps. The MPEG-1 is used for a digital storage medium with a transfer rate of about 1.5 Mbps. The MPEG-2 is applicable to a digital TV or HDTV with a transfer rate of 3 Mbps˜15 Mbps. The H.263 is adapted as a short-term standardization for applications with very low transfer rates less than 64 kbps.
In more detail, the H.263 uses almost the same method as a mixed method of a motion compensation and a DCT used as a moving image compression method of the H.261, MPEG-1, or MPEG-2. It therefore has disadvantages in that a blocking phenomenon is caused in case of highly compressing images in the conventional H.261, MPEG-1, or MPEG-2 system and an image quality of a reproduced image is abruptly degraded.
A video coding method for displaying MPEG-4/H.263-format moving images on an LCD screen of an IMT-2000 terminal performs a coding or encoding operation using a DCT with 8×8-sized image blocks and performs a decoding operation using an IDCT. In this case, the decoding operation is performed using the whole 8×8-sized frequency coefficient block. In this manner, provided that such an IDCT is performed using the whole 8×8-sized frequency coefficient block, a clearly reproduced image can be obtained.
However, in the case where the IDCT is performed using the whole 8×8-sized frequency coefficient block and then a decoding operation is performed, too many calculations are needed and high computational complexity results even though the resulting reproduced image has high quality, such that the above conventional video coding method unavoidably requires both a large amount of memory and a long processing time.